Multiple Input Multiple Output (MIMO) has recently attracted much attention as a broadband wireless mobile communication technology. A MIMO system seeks to increase data communication efficiency by use of a plurality of antennas. Depending on whether the same or different data signals are transmitted through antennas, MIMO techniques may be classified into spatial multiplexing and spatial diversity. In spatial multiplexing, different data signals are transmitted simultaneously through a plurality of Transmission (Tx) antennas such that data can be transmitted at a high rate without increasing a system bandwidth. In spatial diversity, the same data is transmitted through a plurality of Tx antennas, thus achieving transmit diversity. An example of the spatial diversity scheme is space time channel coding.
Depending on whether a receiver feeds back channel information to a transmitter, MIMO techniques may also be classified into open-loop MIMO and closed-loop MIMO. Open-loop MIMO schemes include Bell Labs Layered Space-Time (BLAST) and Space-Time Trellis Coding (STTC). According to BLAST, the transmitter transmits information in parallel and the receiver detects signals by repeating Zero Forcing (ZF) or Minimum Mean Square Error (MMSE) detection such that as much information as the number of Tx antennas can be transmitted. STTC achieves transmit diversity and coding gain by utilizing a space domain. One example of the closed-loop MIMO technique is Transmit Antenna Array (TxAA).
FIG. 1 conceptually illustrates a Coordinated Multi-Point (COMP) scheme of the conventional intra eNBs and inter eNBs.
Referring to FIG. 1, intra enhanced Node Bs (eNBs) 110 and 120 and an inter eNB 130 are present in a multi-cell environment. In a Long Term Evolution (LTE) system, an intra eNB covers a plurality of cells (or sectors). Cells covered by an eNB to which a User Equipment (UE) belongs are in an intra eNB relationship with the UE. That is, cells covered by the same eNB that manages a cell in which a UE is located are cells corresponding to the intra eNBs 110 and 120, and cells covered by a different eNB from the eNB that manages the serving cell of the UE are cells corresponding to the inter eNB 130.
Cells covered by the same eNB that serves a UE exchange information (e.g. data and Channel State Information (CSI)) through an x2 interface, while cells covered by a different eNB from the serving eNB of the UE exchange inter-cell information via a backhaul 140. As illustrated in FIG. 1, a single-cell MIMO user 150 located in a single cell (or sector) may communicate with one serving eNB in the cell (or sector), and a multi-cell MIMO user 160 located at a cell edge may communicate with a plurality of serving eNBs in a plurality of cells (or sectors).
CoMP has been proposed to improve the throughput of a user at a cell edge by applying advanced MIMO in a multi-cell environment. The use of CoMP may reduce Inter-Cell Interference (ICI) in the multi-cell environment. The use of CoMP also allows a UE to receive joint data support from multi-cell eNBs. Also, each eNB may improve system performance by simultaneously supporting one or more UEs (or Mobile Stations (MSs)) MS1, MS2, . . . , MSK using the same radio frequency resources. Further, an eNB may implement Space Division Multiple Access (SDMA) based on CSIs between the eNB and UEs.
The CoMP operation mode may be classified into two modes, a joint processing mode which is cooperative MIMO based on data sharing and a Coordinated Scheduling/Beamforming (CS/CB) mode.
In a CoMP wireless communication system, a serving eNB and one or more cooperating eNBs (or Base Stations (BSs)) BS1, BS2, . . . , BSM are connected to a scheduler over a backbone network. The scheduler receives feedback channel information representing channel states between the UEs MS1 to MSK and the cooperating eNBs BS1, BS2, . . . , BSM, as measured by the eNBs. For example, the scheduler may schedule cooperative MIMO information for the serving eNB and the one or more cooperating eNBs. That is, the scheduler issues a command related to a cooperative MIMO operation directly to each eNB.
However, the current LTE system has not yet defined a method which is to be used for setting serving and neighbor eNBs, information which is to be exchanged, and the like in the case where a CoMP mode scheme is applied to a wireless communication system. In this case, system overload (or overhead) may occur if the serving eNB receives and processes information of all neighbor eNBs from UEs or if the serving eNB transmits all information received from UEs to neighbor eNBs and allows the neighbor eNBs to process all the information.